A racemate is understood to mean an equimolar mixture of two enantiomers. Enantiomers are isomers, that is to say substances which do not differ with regard to the overall formula but rather only in the arrangement of the atoms. In the case of enantiomers, the difference lies in the chirality, i.e. in the property of behaving like an image and mirror image relative to one another.
A separation of these racemic mixtures, which will be referred to below as racemate separation, is usually difficult since the chemical and physical properties of the enantiomers are identical apart from their behavior in relation to linearly polarized light and other chiral substances.
Many pharmaceutically active substances are chiral. Often, however, only one of the two enantiomers can be used as an active substance since the physiological effects of the enantiomers on the human organism usually differ from one another. In addition, the obtaining of pure enantiomers is also highly important in agrochemistry and in the food industry. The market for enantiomeric substances (in pharmaceutically active substances, plant protection agents, dyes and fragrance compounds) has increased considerably in recent years.
One method for racemate separation which is known from the prior art is referred to as preferred crystallization. However, according to the prior art, this method can be used only for so-called conglomerate-forming substance systems, i.e. for those systems in which the enantiomers are immiscible in the solid phase. On the contrary, preferred crystallization cannot to date be used for compound-forming substance systems, which are much more common.
Only around 5-10% of all chiral systems are conglomerate-forming systems, whereas most of the remaining systems are compound-forming systems. For thermodynamic reasons, these systems cannot be separated starting from the racemate by means of preferred crystallization.
Other possibilities for racemate separation are known from the prior art. These possibilities include e.g. chemical methods, in which firstly diastereomers are formed, biochemical methods, i.e. methods which are carried out using microorganisms or enzymes, or chromatographic methods. In general, preferred crystallization offers advantages over these methods.